Ditto to mgourley, but maybe I can provide some generic ideas. Bear in mind Ipacy that I don't know if you're under any FS standard (such as SQF), which will change the answers provided.
For my packaging suppliers, instead of a constant verification that each sanitation was effective, I asked for an annual validation/verification that the methods used were effective. E.g they would take an obviously dirty line, swab it for indicator organisms, then use their cleaning method, then swab again to ensure that the method used was effective at removing those microorganisms. Microbial data that demonstrates your methods are effective is more valuable than random swabbing IMO. I ask my suppliers to do this once per year for something like 5 surfaces, comes out to $100-200 in testing fees.
In response to testing your products, it's hard to say how helpful that would be. Suppliers obviously like more data over less, but my primary concern with packaging is that it becomes contaminated on an infrequent basis due to poor sanitation/GMP's in the facility (since FDA does not inspect). "End-item" testing does not help with this.
Finally, since you mentioned paperboard, a helpful microbial standard would be the paperboard "disintegration" standard in the raw milk ordinance of 250CFU/gram, which any dairies you may sell to are required to meet:
1. Paper stock shall meet the bacteriological standard of not more than two hundred fifty (250) colonies per gram as determined by the disintegration test. The paper stock supplier shall certify that their paper stock was manufactured in compliance with this Standard. This applies only to the paper stock prior to lamination.
